The golden tree (Cassia fistula L.) is a tropical and subtropical legume tree that is used as an ornamental, for fodder and for fuel and timber.

Morphology

Cassia fistula is a medium sized deciduous or semi-deciduous tree, 10 to 15 m tall with a straight trunk to 5 m in height and 1 m in diameter. It has spreading branches that form an open crown. The stem bark is pale grey, smooth and slender when young and dark brown and rough when old. The leaves are alternate, spirally arranged, paripinnately compound, 30-40 cm long, each pinnae bearing 3-8 pairs of large, ovate leaflets, 7.5-15 cm long x 2-5 cm broad, entire. The flowers are showy, bright yellow in colour, pentamerous and slightly zygomorphic in shape, 3.5 cm in diameter. They are borne on terminal, drooping racemes about 30-60 cm long which can be grouped by 3. The fruit is a pendulous, cylindrical, indehiscent pod, up to 60-100 cm long x 1.5-2 cm wide. It is black, glabrous and many seeded (25-100 seeds). When the pods are still young, the seeds are embedded in a black pulp. The seeds are ellipsoid, 8-9 mm long, glossy light brown in colour (Orwa et al., 2009; Bosch, 2007). The latin name "cassia" comes from the greek word "kassia" meaning fragrant and aromatic plant (Datiles et al., 2017; Orwa et al., 2009).

Uses

Cassia fistula is a multipurpose tree. It is widely grown as an ornamental plant in tropical and subtropical areas due to its profuse flowering. The flower of the golden tree is Thailand's national symbol (Royal Thai Government, 2001) and the state flower of the Kerala state in India. Cassia fistula provides fuel and good quality charcoal, as well as a hard and heavy timber suited to make furniture, farm implements, posts, wheels and mortars. The bark yields tannins and dyestuff. The flowers produce pollen and the base of the leaf-stalk yields a nectar that is collected by bees. In India, some people eat the flowers (Orwa et al., 2009). Golden tree twigs are commonly lopped for fodder (Göhl, 1982). Cassia fistula features extensively in ethnomedicine. Leaf extracts are known for their antidiarrhoeal activity demonstrated in laboratory studies with rabbits or guinea pigs (Gupta et al., 1993). Some extracts of leaves and flowers have a significant antibacterial activity and other valuable pharmacological activities, and are thus used in traditional South Asian pharmacopoeia (Gobianand et al., 2010; Voon et al., 2012).

Distribution

Cassia fistula is thought to have originated from South-East Asia, and was introduced throughout the tropics. Golden trees have escaped cultivation in Costa Rica, Guyana, and French Guiana (Boggan et al., 1997), and are naturalized in many parts of the tropics including the West Indies, Mexico, Ecuador, Belize, and parts of Micronesia. It is considered as an invasive in Queensland, Australia (Datiles et al., 2017).

Cassia fistula is a tree of deciduous forests ranging from tropical to moist through subtropical forest zones. It is found from sea level up to an altitude of 1300 m. It occurs on dry, shallow mountain slopes as well as on better sites (Ecocrop, 2017). The golden tree can grow where rainfall is between 480 and 2720 mm, and where annual temperature ranges from 18 to 29°C. It grows on a wide range of soils including sandy and loamy soils with pH from 5.5 to 8.7, though it does better on calcareous soils and red volcanic soils. The tree can withstand moderate amount of shade, is drought resistant, but not frost hardy (Bosch, 2007). It is not an N-fixing tree (Datiles et al., 2017).

Forage management

Propagation of Cassia fistula is mainly done by seeds. Seeds have long survival and their viability can be maintained for more than 3 years in hermetic storage at room temperature with 13 ± 2% moisture content. Seeds previously soaked in sulphuric acid or manually scarified can be directly sown or planted in containers. Seedlings raised in containers will be ready for planting out after 2-3 years. During the first stages of growth, seedlings require large amount of water. The golden tree is a slow growing tree that sheds its leaves every 9-10 months. It may require 8-9 years before first flowering and pod production. The tree coppices vigorously and produces root suckers freely. Vegetative propagation may reduce timelaps to flowering (Bosch, 2007).

Environmental impact

Revegetation

Invasiveness

Cassia fistula produces large amounts of seeds that remain viable for more than a year, and is also able to propagate through cuttings and layering, and is tolerant of a wide range of soils and climate. It has been reported to be invasive in Queensland, Australia. It could have a negative environmental impact given its wide distribution range (Datiles et al., 2017).

Cassia fistula remains little studied in ruminant feeding although it seems to be a good legume tree as protein source. It can be used for supplementing ruminants fed with low quality forages.

Sheep and goats

In Egypt, golden tree leaves offered to sheep and goats as sole forage with 10 g concentrate/kg body weight resulted in a higher forage dry matter intake (DMI) in sheep than in goats (21.4 vs. 20.4 g/kg BW0.75). The addition of a small amount (10 g/d) of polyethylene glycol (PEG), which is known to alleviate the negative effect of tannins on intake and digestibility, increased DMI in both species. DM digestibility of the diet was 51% and 56% for sheep and goats, respectively. Although there was no effect of PEG on DM digestibility in both species, protein digestibility increased with PEG from 52% to 54% in sheep, and from 57% to 61% in goats (Salem et al., 2006).

Cattle

In Colombia, golden tree leaves offered to grazing zebu males (370 kg) as a supplement (10% of the diet) resulted in a higher daily weight gain (1360 g/d vs. 1133 g/d without supplement) during the rainy season. However, during the dry season, Cassia fistula leaves were not well consumed and contained high levels of total phenolic compounds and the daily weight gain was almost null (-20 g/d) compared to animals without supplement (220 g/d) (Apraez et al., 2017).

Rabbits

No study on the use of Cassia fistula leaves as potential forage in rabbit feeding seems available (as of 2013). However, a strong antifertility activity of leaves or seeds extracts was observed in the male and the female rat (Priya et al., 2012a; Priya et al., 2012b), so the use of leaves or other parts of this tree are not recommended in rabbit feeding until feeding trials demonstrate their suitability as a feed.